Interesting question Safaa, that's exactly what I'm looking to do, and the Dataform module is the only one I found that could give somebody the right to give grade to somebody else easily with many items like you and me whant to do. To say the truth, your Excel form show something similar to what I whant to achieve.
There is probably a better way to do so, i.e. with JS, but my knowledges are not enough good on this field to go there without help. If anybody have ideas, I'm open.
As you say, the Doc for this module look sometimes slim, but I think Itamar make a pretty job on it and on the module itself. As you said Itamar, it's also up to us to jump in and add some lines. I plan to do so if I finaly decide to use the Dataform module for my project... If I'm not so good to write lines of code, I'm not to bad on plain text